What is fuel cut? [Community Project]

Craig

Craig

Lifer
Hello fellow TGTTers.

I am putting forward a proposal here to help answer the all too common question of fuel cut (something that has seen a recent rise in posts). I had planned on doing a big write up on it, however, I'm too busy and I think it would be good to get the views of other members too.

The Idea:

This thread is used for the experienced and knowledgable members to post up information regarding fuel cut. The causes, the cures, the common incorrect "cures" given etc etc...

Once sufficient information is provided in here, an "article" will be written up as a new thread (I'm more than happy to do this, credit will be given to all contributors) which is a compilation of all the facts given in this thread. This will be placed in the "Awesomely helpful info" section. Then when the inevitable happens (someone asks a question on the matter without searching), they can be referred to the master thread which will only contain accurate information.

If successful, we can then look at working together on other common issues. There is a ridiculous amount of knowledge on this forum, and I think it would be good to compile this and have it stored in the forum mentioned above, which is rather unpopulated!

If this is a bad idea, delete it mods :D.
 
Craig

Craig

Lifer
I'll get the ball rolling then with some topic sections . Please list the section under which your facts should fall. If the section required is not there, make up a suitable section name.

What is fuel cut?
What causes fuel cut to happen?
How do I know if I've hit fuel cut?
How can I solve the problem?
Will fuel cut damage my car?
Common incorrect solutions.


Even if you only have a small piece of information on one of the sections, post it up in as much detail as possible. Each piece will go towards making the final draft.
 
lingl9z

lingl9z

Member +
What Is Fuel Cut?​
Fuel cut occurs when the firing signal stops being sent from the ECU to the injectors meaning exactly what the title says "Fuel Cut"


Whats The Cause?​

Although alot of assumptions are thrown around I believe from what I've read that fuel cut isnt caused by, small injectors, low fuel pressure, free flowing exaust, larger turbo's or running no air filter. Yes some of these can display the symptons but it's not the direct cause.

The actual cause is the ECU seeing more air entering the intake/engine than it was programmed to do in the factory, which in tern was programmed to run the injectors to a certain duty cycle.

Why Am I Getting Fuel Cut?​
The reason your getting fuel cut is because the ECU's seeing too much air in the system that it's meant to. Basically any modification you do to the engine that gives a power increase can make fuel cut occur.

- Open or relocated filters
- Free Flowing Exhaust system/Side Exit.
- Upping the boost on a turbo that can't vent it quick enough so get's boost creep meaning boost rises past the set level meaning more air, not enough fuel - Fuel Cut.

How do I get rid of fuel cut?​

A lot of people often see HKS/JAM Fuel cut defenders and immidatly think and are often told that if they install a FCD they won't get fuel cut anymore... This only mask's the problem as the engine will be getting alot of air but won't have the fueling to match which intern makes the engine run LEAN!

An engine running lean won't last very long before it goes... BANG! search the forum and you'll see a large amount of threads related to this.



Temp fixes - Preventing fuel cut?​

A temp fix isn't ideal but can be pretty useful if you don't have money to hand.

- Lose lead foot syndrome.

Self explanitory really.

- Reduce the amount of air coming in.

If you have a meshed filter or open filter, Put the EFI pipe back on with the standard box or even tape half the filter up to reduce the amount of air that can be taken in.

- Boost Creep

If your car's creeping port the wastegate with a dremel or like if possible.

Perminatly prevent Fuel Cut.​

Either reduce the amount of air the ECU see's or Increase the amount of fuel going to the engine. This can be done in a series of ways.

1 - by fitting an RRFRP (Rising Rate Fuel Pressure Regulator) This basically allows you to adjust the fuel pressure allowing more to flow in the right direction. Once you've fitted the RRFRP you'll need to install an FCD and get it set up on a rolling road with a wide band.

2 - Get a piggy back ECU and get it mapped (the likes of Emange)

3 - Get a standalone ECU like Jam, Blitz etc.


DO NOTS.​

Do not fit an FCD without correct fueling mods.
Do not fit an rrfrp to adjust the pressure without checking AFRS.
Do not fit larger injectors.

Okay I hope this is a worthy contribution - My PC doesn't have spell checker on at the min and I'm over tired - Please excuse the spellinga.
 
Last edited:
Texx

Texx

Super Moderator
http://www.toyotagtturbo.com/forums/showthread.php?t=44052

Monkfish said:
What is fuel cut?

Fuel cut is exactly what it says on the tin, the fuel supply is cut to the engine. But why does it do this? Read on, young Padawan.

Whilst the engine is running, the ECU is monitoring various (Read: Lots!) of things going on in the engine with a plethora of sensors. It monitors things such as air:fuel ratio, rpm, temps and all manner of other things I'll not go into now. Basically, it knows how much fuel it needs and how much it is throwing through the injectors. Fuel cut is basically a fail safe. If you modify an engine (For example, increasing the boost for more power) you'll get to a point, about 0.8 Bar from memory, where the ECU basically says "Hang on, if you run the boost any higher without more fuel, bad shit is going to happen" and it then cuts the fuel to the engine entirely to prevent it running lean and causing detonation.

What you'll experience when you're driving is a sudden loss of all power (It'll feel like you've driven into a wall), lots of lurching about and the engine management will light up (as well as your underpants if it's the first time :haha:). After some careful driving, the engine management light will go out and all will return to normal. Constantly hitting fuel cut will also damage your engine, so if you do keep cutting, you need to find out why if you don't know and rectify the issue. You can also get fuel cut on a cold night if you're running boost close to the cut level and are getting creep.

To remove the fuel cut, you need a fuel cut defender which basically tricks the engine into thinking all is well and it'll not fuel cut. Important note: Simply removing the fuel cut without the supporting modifications will cause your engine internals to have and argument with the block and depart. Violently. Please take the time to read through this article in this topic before you proceed.
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